Move corosync-notifyd policy file into $(datadir)/dbus-1/system.d

As per dbus-daemon(1):

Third-party packages would historically install XML files into
/etc/dbus-1/system.d, but this practice is now considered to be
deprecated: that directory should be treated as reserved for the
system administrator.

Signed-off-by: Ferenc Wágner <wferi@debian.org>
Reviewed-by: Jan Friesse <jfriesse@redhat.com>